This invention relates to apparatus and methods for transmitting data. More particularly, the invention concerns apparatus and methods for reducing noise in transmitted data.
In a traditional xe2x80x9csingle-endedxe2x80x9d data transmission system, a varying data signal is sent over a communication channel by varying a signal attribute, such as current or voltage. For example, in digital data transmission, sending a 0 volt signal may indicate a logic level low (i.e. a digital zero bit), while sending a 5 volt signal may indicate a logic level high (i.e. a digital one bit). This conventional method of data transmission is adequate if the signal levels are widely spaced and well defined. However, power consumption by electronic devices is a major issue. To address the power consumption concern, the supply voltages and the separation between different data levels has been significantly reduced. Unfortunately, single-ended data transfers are relatively susceptible to noise when data level separation is reduced. Even small amounts of noise can seriously degrade the reliability of a single-ended data transmission system having reduced data level separation.
A conventional solution to noise degradation is to use a differential mode of signaling. In differential signaling, a single data signal is transmitted over two wires, each of which carries one signal component. The two components are generally derived from the same source data signal and are varied such that the data signal is transmitted as the difference between the two signal components. In digital environments, differential data signals are typically transmitted as two voltage signals of opposite polarity relative to a reference level. The transmitted data is extracted by determining which signal components has a greater voltage.
Differential mode signaling provides for improved noise immunity and greater noise tolerance, and is therefore widely used to interconnect digital circuits on separate chips and circuit boards. However, a significant problem with differential signaling is that two wires are required to transmit one data signal.
Accordingly, it is desirable to improve the ratio of transmitted data signals to wires used, while retaining the good noise immunity associated with standard two-wire differential signaling.
Digital data can be transmitted in a noisy environment with a degree of noise immunity, according to the invention, by transmitting a digital data signal, generating a reference signal and transmitting the generated reference signal. The reference signal has a voltage level between a logic level low and a logic level high of the digital data signal.
Another embodiment of the invention provides for an integrated circuit having a transmitter for transmitting a digital data signal, and a reference circuit for generating and transmitting a reference signal. The generated reference signal has a voltage level between a logic level low and a logic level high of the digital data signal.
In accordance with a further embodiment of the invention, a receiver is provided for receiving a digital signal and a reference signal. The receiver includes a switch circuit and a comparator. The switch circuit generates a switching point signal as a function of the reference signal, and the switching point signal identifies the transition between a logic level low and a logic level high in the received digital signal. The comparator compares the received digital signal with the switching point signal. Based on this comparison, the comparator determines whether the received digital signal is a logic level low or a logic level high.